Breast cancer is the most common type of cancer and the second most common cancer-related deaths in women in the United States. Among the two major breast cancer subsets of estrogen receptor-negative (ER−) and ER-positive (ER+) tumors, the ER− patients has been recognized as the more aggressive subtype, more difficult to treat, greater ethnic disparity, worse prognosis, and almost twice the risk of mortality than ER+ tumors.
Thus there is an urgent need to identify novel indicators for ER− breast cancer prognosis.